This invention relates to radar target-to-fuze range sensing fuzes, and more particularly to a system for electronic counter-countermeasures (ECCM) for fuzes.
Radar range sensing fuzes operating in hostile environments are often subjected to a variety of electronic techniques often referred to as electronic countermeasures (ECM) which are intended to interfere with the proper operation of the fuzing system. From a radar fuzing standpoint ECM equipment can be classified in two general groups according to the intended purpose of the interference: (1) Dud Jammers designed to mask the intended signal by increasing the background clutter in the fuze receiver to desensitize the fuze to its own return signals (for example a high-powered CW transmitter modulated by noise), and (2) Early Jammers designed to generate deceptive signals that appear to the fuze as valid echoes from the intended target. The Early Jammer attempts to evoke premature or early fire commands in the fuze at ranges significantly beyond the desired warhead function range. An example might be a repeater jammer, which in addition to receiving, amplifying, and retransmitting a detected fuze signal, might impose additional intelligent modulation to the signal. Prior detailed knowledge of the electrical characteristic of the fuze is a primary tool employed by the Early Jammer designer or operator in the modulation effort.
This invention is an effective radar fuzing method which counters both types of Early Jammers, the out-of-spectrum early jammer, which exploits the AM detection characteristic of the fuze mixer, and the repeater early jammer that falsely produces an in-band signal spectrum simulating a valid target return signal.
It is therefore a primary object of this invention to provide a system for recognizing false signals produced by out-of-spectrum and repeater-type jammers.
Another object of the invention is to desensitize the fuze during the time the jammers are effective.
Yet another object of this invention is to actuate the fuze to fire when the fuze-to-jammer range reaches a predetermined range regardless of the presence of jamming signals.